Offset printing presses are well known in the art. Typically, water and ink are supplied to a printing plate cylinder, and are then transferred to a blanket cylinder for printing onto sheets or web, fed between the blanket cylinder and an impression cylinder. The water supply to the plate cylinder usually comprises a dampening unit having a dampening form roller which contacts the plate cylinder and is fed water from a water pan through intermediate water transferring rollers. Similarly, an inking unit transfers ink from an ink supply to the plate cylinder through an ink transfer and application rollers.
While such presses have fixed lateral dimensions, and as such printed products wider than the length of the cylinders cannot be produced, the circumference of the rotating cylinders determines the length of each repeated pattern being printed onto the web or sheets passing therethrough. Accordingly, the larger the circumference of the plate and blanket cylinders being used, the longer the printed pattern that can be produced. Therefore, in order to permit a press to be modified to permit printing of difference sized “repeats”, or each repeated pattern that is printed onto the web for each revolution of the cylinders, it is desirable to be able to use plate and blanket cylinders of different circumferences in order to be able to vary the repeat size provided by the press.
To achieve this desired press convertibility, it has been know to provide an offset press with a removable cylinder cartridge, having at least the plate and blanket cylinders mounted therein. For such a cartridge to be removed from the rest of the printing press, the cylinders must be disengaged from one another, and the entire cartridge is slid out as a single unit from the frame of the press. A replacement cartridge having therein plate and blanket cylinders of a smaller or larger circumference, is then inserted into the press in place of the original cartridge. This therefore permits the press to be converted to change the size of the repeat produced with each rotation of the press cylinders. While this solution provides the press with repeat size flexibility, each cartridge is large and costly, and therefore the practical range of flexibility is generally limited by the cost and space considerations of keeping many different cartridges having cylinders of various sizes.
Various printing presses having removable cylinders are also known. However, to permit the removal of the cylinders requires them to be disengageable from one another. The precisely set contact stripe between the cylinders is therefore often lost. Further, this typically also requires that the intermeshed gears driving the cylinders can be completely disengaged from each other every time a cylinder is to be removed, and easily re-engaged once a new replacement cylinder is introduced into the press. A known way to avoid this problem is to completely replace the gear train by drive motors used to drive the cylinders at the necessary speeds. Particularly, some presses employ a drive motor for each cylinder, thereby circumventing the requirement of gear trains completely. However, printing presses which are completely driven by servo drive systems are more expensive and more complex than those which use traditional gear train drives. Further, if any of the drive motors are incorrectly set or malfunction, the resultant mismatch in cylinder speeds can cause defective printed product or damage to the press.